Attractive Electrostatic Interactions Research Articles

Dual-functional adsorptive membranes for PFAS removal: Mechanism, CFD simulation, and selective enrichment

The remediation of emerging water contaminants, particularly per- and polyfluoroalkyl substances (PFAS), presents challenges due to their refractory nature and the presence of competing substances. Dual-functional adsorptive membranes, with hydrophobic backbone and quaternary ammonium moieties, were thereby designed to selectively intercept organic competitors while enrich PFAS. A 96.8 % removal of perfluorooctanoic acid (PFOA) was achieved and this effective removal (>90 %) maintained across five reuse cycles with a total treatment capacity of 650 L m−2. Rather than the rejection mechanism of nanofiltration process, these adsorptive membranes utilize synergistic electrostatic attraction and hydrophobic interactions, leading to a greater enrichment factor of 18.5 (PFOA over humic acid) and a permeability of 34.6 L m-2h−1 bar−1 (1.9- and 4.5-fold higher than reported NF 270 membranes, respectively). Furthermore, computational fluid dynamics (CFD) modeling revealed that the sponge-like matrix effectively prevents channeling flow and enhance access to adsorption sites. Sensitivity analysis and the high Damkohler number indicated that the adsorption process is mass transfer-controlled, with the key parameters ranked in order of significance: residence time > fluid viscosity > intrinsic adsorption rate. With consistent removal performance with co-existing competitors, efficient regeneration, and reusability, the dual-functional adsorptive membranes offer promising practical efficacy for PFAS remediation.

Adsorption characteristics and mechanism of novel ink melanin composite modified chitosan for Cd(II) in water

In this study, chitosan (CS), carboxymethyl chitosan (CMCS), and chitosan quaternary ammonium salt (HACC) were successfully loaded with ink melanin (ME) as efficient adsorbents for Cd(II) removal. The results of batch adsorption experiments and structural characterization showed that the modified CS loaded with ME improved the adsorption capacity of the composites for Cd(II). The pseudo-second-order kinetic and Langmuir equations were better suited to describe the batch adsorption experiments. The adsorption of Cd(II) was chemisorption with desirable adsorption effect when the concentration of the three composites was 0.5 mg/mL and the pH value was neutral. Among them, HACC-ME demonstrated remarkable Cd(II) adsorption performance (107.18 mg/g) and sustained an 85 % efficiency in Cd(II) removal over five adsorption-desorption cycles. Ion exchange, complexation, electrostatic attraction, and hydrophobic interaction were the primary mechanisms for Cd(II) removal. Overall, HACC-ME could be employed as a low-cost and highly efficient new natural adsorbent material for the removal of Cd(II) ions from wastewater. These findings illuminate pathways for the development of efficient and novel natural adsorbent materials for environmental cleanup purposes.

Unveiling the Singular Conformation of the 3‐Fluoropyrrolidinium Cation

AbstractThe pyrrolidine ring is a 5‐membered ring that holds significant importance in biological chemistry. The introduction of fluorine at position 3 of pyrrolidine results in pseudo‐axial and pseudo‐equatorial C−F bonds. However, both quantum‐chemical calculations and infrared spectroscopy reveal that the 3‐fluoropyrrolidinium cation only adopts one conformation, with the C−F bond in the pseudo‐axial orientation. Upon deprotonation of 3‐fluoropyrrolidinium, leading to the formation of 3‐fluoropyrrolidine, four conformations are predicted based on CCSD/DGTZVP quantum‐chemical calculations. Among these, the conformation favoring an N−H⋅⋅⋅F−C interaction emerges as the most stable, both in the gas phase and within an implicit DMSO medium. The heightened ring puckering observed in 3‐fluoropyrrolidinium compared to the most stable conformation of 3‐fluoropyrrolidine suggests that the singular conformation of the cation arises from a robust attractive electrostatic interaction resembling hydrogen bonding, rather than a charge‐dipole gauche effect as previously assumed.

Development of Recoverable Magnetic Bimetallic ZIF-67 (Co/Cu) Adsorbent and Its Enhanced Selective Adsorption of Organic Dyes in Wastewater.

In the critical domain of wastewater treatment, the development of cost-effective, durable, and recyclable adsorbents with high adsorption capacities remains a significant challenge. This study introduces a novel magnetic bimetallic Metal-Organic Framework (MOF) adsorbent, MZIF-67-Co/Cu, doped with copper ions. The MZIF-67-Co/Cu adsorbent was successfully synthesized and structurally characterized, demonstrating remarkable selectivity for removing methyl orange (MO) from water. This high selectivity is attributed to the adsorbent's high porosity and Lewis base properties at the coordinating metal ion center. The incorporation of Cu ions significantly enhances the porous architecture and increases the number of metal adsorption sites, leading to an impressive maximum MO adsorption capacity of 39.02 mg/g under optimized conditions (0.5 g/L adsorbent concentration, pH 3.0, 250 rpm agitation speed, adsorption time > 10 min). The adsorption kinetics closely follow the pseudo-second-order model, and the isotherm data fit well with the Langmuir model. The primary adsorption mechanisms involve electrostatic attraction and mesoporous interaction. This study highlights MZIF-67-Co/Cu as a highly efficient adsorbent with magnetic recovery capabilities, positioning it as a promising candidate for addressing critical issues in wastewater treatment.

Thermo- and pH-Responsible Gels for Efficient Protein Adsorption and Desorption

Protein adsorption behavior was examined on poly(N-isopropylacrylamide-co-sodium methacrylate)-based hydrogels at different temperatures: 5, 20, and 37 °C, and pH: 4.5, 7, and 9.2. The hydrogels, whose covalent skeleton contains pendant anionic units due to the presence of the sodium methacrylate co-monomer, exhibited both thermo- and pH-sensitivity with different extents, which depended on the content of ionizable moieties and the cross-linker density. The hydrogel composition, temperature, and pH influenced the zeta potential of the hydrogels and their swelling properties. The proteins selected for the study, i.e., bovine serum albumin (BSA), ovalbumin (OVA), lysozyme (LYZ), and a monoclonal antibody (mAb2), differed in their aminoacidic composition and conformation, thus in isoelectric point, molecular weight, electrostatic charge, and hydrophobicity. Therefore, the response of their adsorption behavior to changes in the solution properties and the hydrogel composition was different. LYZ exhibited the strongest adsorption of all proteins with a maximum at pH 7 (189.5 mg ggel−1); adsorption of BSA and OVA reached maximum at pH 4.5 (24.4 and 23.5 mg ggel−1), whereas mAb2 was strongly adsorbed at 9.2 (21.7 mg ggel−1). This indicated the possibility of using the hydrogels for pH-mediated separation of proteins differing in charge under mild conditions in a water-rich environment of both the liquid solution and the adsorbed phase. The adsorption affinity of all proteins increased with temperature, which was attributed to the synergistic effects of attractive electrostatic and hydrophobic interactions. That effect was particularly marked for mAb2, for which the temperature change from 5 to 37 °C caused a twentyfold increase in adsorption. In all cases, the proteins could be released from the hydrogel surface by a reduction in temperature, an increase in pH, or a combination of both. This allows for the elimination of the use of salt solution as a desorbing agent, whose presence renders the recycling of buffering solutions difficult.

Selective adsorption behaviors and mechanisms of benzyl quaternary ammonium salt on quartz and gypsum: A combined experimental and theoretical study

Benzyl quaternary ammonium salt is an effective collector of quartz from gypsum. To investigate the selective collection mechanism of tetradecyl dimethyl benzyl ammonium chloride (TDBAC) for quartz from a microscopic view, the adsorption experiments, first-principles calculations based on density functional theory (DFT), and molecular dynamics (MD) simulation were performed in this work. The adsorption experiment results show that the adsorption capacity of TDBAC on the quartz surface was 1.6 × 10−6 mol/m2, much larger than that on the gypsum surface (1.0 × 10−7 mol/m2). The interaction energy of TDBAC with quartz surface was −20202.98 kJ/mol, much smaller than that with gypsum surface (-78.37 kJ/mol). DFT calculation results indicate that the quartz surface was more likely to interact with TDBAC through electrostatic attraction since the average negative charge and exposure oxygen density of the quartz surface were both greater than those of the gypsum surface. After the adsorption of TDBAC, there were hydrogen bonds formed between the hydrogen atoms in TDBAC and the oxygen atoms on the quartz surface. This work confirmed that the highly selective adsorption of TDBAC on quartz surface was attributed to the strong electrostatic attraction and hydrogen-bond interaction.

Oral food-derived whey protein isolate-Tremella fuciformis polysaccharides pickering emulsions with adhesive ability to delivery magnolol for targeted treatment of ulcerative colitis

Magnolol (Mag) is a promising natural compound with therapeutic potential for ulcerative colitis (UC). Here we designed and fabricated an oral food-grade whey protein isolate-Tremella fuciformis polysaccharides (WPI-TFPS) stabilized pickering emulsions to encapsulate Mag (Mag-WPI-TFPS) for targeted treatment of UC. With the assistance of the WPI-TFPS, pickering emulsions were well encapsulated and formed stable microparticles with a particle size of approximately 9.49 ± 0.047 μm, a 93.63 ± 0.21 % encapsulation efficiency and a loading efficiency of 21.53 ± 0.01 %. In vitro, the formulation exhibited sustained-release properties in simulated colon fluid with a cumulative release rate of 60.78 % at 48 h. In vivo, the Mag-WPI-TFPS specifically accumulated in the colon tissue for 24 h with stronger fluorescence intensity, which demonstrated that TFPS and WPI had a good adherence ability to inflamed mucosa by electrostatic attraction and ligand-receptor interactions. As expected, compared with Free-Mag, the oral administration of Mag-WPI-TFPS remarkably alleviated the symptoms of UC and protected the colon tissue in DSS-induced UC mice. More importantly, WPI-TFPS enhanced gut microbiota balance by increasing the diversity and relative abundances of Lactobacillaceae and Firmicutes. Overall, this study presents a convenient, eco-friendly, food-derived oral formulation with potential as a dietary supplement for targeted UC treatment.

Adsorption of Acacia Gum on Self-Assembled Monolayer Surfaces: A Comprehensive Study Using QCM-D and MP-SPR.

The interfacial structuring of Acacia gum at various pH values on self-assembled monolayer (SAM) surfaces was investigated in order to evaluate the respective importance of surface versus biopolymer hydration in the adsorption process of the gum. To this end, SAMs with four different ending chemical functionalities (-CH3, -OH, -COOH, and -NH2) were used on gold surfaces, and the gum adsorption was monitored using multiparametric surface plasmon resonance (MP-SPR) and quartz crystal microbalance with dissipation. Surface modification with alkanethiol and the subsequent adsorption of Acacia gum were also characterized by contact angle measurements using both sessile drop and captive bubble methods. According to MP-SPR results, this study demonstrated that gum adsorbed on all surfaces and that adsorption is the most favorable at both acid pH and hydrophobic environments, i.e., when both the surface and the biopolymer are weakly hydrated and more prone to interfacial dehydration. These results reinforce our recent proposal of interfacial dehydration-induced structuring of biopolymers. Increasing the pH logically decreased the adsorption capacity, especially on a hydrophilic surface, enhancing the hydration rate of the layer. A hydrophilic surface is unfavorable to Acacia gum adsorption except if the surface presents a negative surface charge. In this case, interfacial charge dehydration was promoted by attractive electrostatic interactions between the surface and biopolymers. In the aggregate, the water percentage and the viscoelastic properties were closely related to the properties of the surface function: the negative charge and hydrophobicity significantly increased the hydration rate and viscoelastic properties with the pH, while the positive charge induced a rigid and more dehydrated layer.

Preparation of Water-Soluble Polyion Complex (PIC) Micelles with pH-Responsive Carboxybetaine Block.

A dual zwitterionic diblock copolymer (M100C100) consisting of poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC, M) and poly(3-((2-(methacryloyloxy)ethyl) dimethylammonio) propionate) (PCBMA, C) is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. A double hydrophilic diblock copolymer (M100S100) consist of PMPC and anionic poly(3-sulfopropyl methacrylate potassium salt) (PMPS, S) is synthesized via RAFT. The degrees of polymerization of each block are 100. The charges of PMPC are neutralized intramolecularly. At neutral pH, the charges in PCBMA are also neutralized intramolecularly due to its carboxybetaine structure. Under acidic conditions, PCBMA exhibits polycation behavior as the pendant carboxy groups become protonated, forming cationic tertiary amine groups. PMPS shows permanent anionic nature independent of pH. Charge neutralized mixture of cationic M100C100 and anionic M100S100 in acidic aqueous solution forms water-soluble polyion complex (PIC) micelle owing to electrostatic attractive interactions. The core is composed of the cationic PCBMA and anionic PMPS blocks, with the PMPC blocks serving as shells that covered the core surface, forming spherical core-shell PIC micelles. Above pH 4 the pendant carboxy groups in PCBMA undergo deprotonation, transitioning to a zwitterionic state, thereby eliminating the cationic charge in PCBMA. Therefore, above pH 4 the PIC micelles are dissociated due to the disappearance of the charge interactions.

Controlling DNA Fragments Translocation across Nanopores with the Synergic Use of Site-Directed Mutagenesis, pH-Dependent Charge Tuning, and Electroosmotic Flow.

Biological and solid-state nanopores are at the core of transformative techniques and nanodevices, democratizing the examination of matter and biochemical reactions at the single-molecule level, with low cost, portability, and simplicity in operation. One of the crucial hurdles in such endeavors is the fast analyte translocation, which limits characterization, and a rich number of strategies have been explored over the years to overcome this. Here, by site-directed mutagenesis on the α-hemolysin protein nanopore (α-HL), sought to replace selected amino acids with glycine, electrostatic binding sites were induced on the nanopore's vestibule and constriction region and achieved in the most favorable case a 20-fold increase in the translocation time of short single-stranded DNA (ssDNA) at neutral pH, with respect to the wild-type (WT) nanopore. We demonstrated an efficient tool of controlling the ssDNA translocation time, via the interplay between the nanopore-ssDNA surface electrostatic interactions and electroosmotic flow, all mediated by the pH-dependent ionization of amino acids lining the nanopore's translocation pathway. Our data also reveal the nonmonotonic, pH-induced alteration of ssDNA average translocation time. Unlike mildly acidic conditions (pH ∼ 4.7), at a pH ∼ 2.8 maintained symmetrically or asymmetrically across the WT α-HL, we evidenced the manifestation of a dominant electroosmotic flow, determining the speeding up of the ssDNA translocation across the nanopore by counteracting the ssDNA-nanopore attractive electrostatic interactions. We envision potential applications of the presented approach by enabling easy-to-use, real-time detection of short ssDNA sequences, without the need for complex biochemical modifications to the nanopore to mitigate the fast translocation of such sequences.

Complexes of Zinc-Coordinated Heteroaromatic N-Oxides with Pyrene: Lewis Acid Effects on the Multicenter Donor-Acceptor Bonding.

4-Nitroquinoline-N-oxide (NQO) and 4-nitropyridine-N-oxide (NPO) are important precursors for the synthesis of substituted heterocycles while NQO is a popular model mutagen and carcinogen broadly used in cancer research; intermolecular interactions are critical for their reactions or functioning in vivo. Herein, the effects of the coordination of N-oxide's oxygen atom to Lewis acids on multicenter donor-acceptor bonding were explored via a combination of experimental and computational studies of the complexes of NQO and NPO with a typical π-electron donor, pyrene. Coordination with ZnCl2 increased the positive electrostatic potentials on the surfaces of these π-acceptors and lowered the energy of their LUMO. Analogous effects were observed upon the protonation of the N-oxides' oxygen or bonding with boron trifluoride. The interaction of ZnCl2, NPO, or NQO and pyrene resulted in the formation of dark co-crystals comprising π-stacked Zn-coordinated N-oxides and pyrene similar to that found with protonated or (reported earlier) BF3-bonded N-oxides. Computational studies indicated that the coordination of N-oxides to zinc(II), BF3, or protonation led to the strengthening of the multicenter bonding of the nitro-heterocycle with pyrene, and this effect was related both to the increased electrostatic attraction and molecular-orbital interactions in their complexes.

Chalcogen Noncovalent Interactions between Diazines and Sulfur Oxides in Supramolecular Circular Chains.

The noncovalent chalcogen interaction between SO2/SO3 and diazines was studied through a dispersion-corrected DFT Kohn-Sham molecular orbital together with quantitative energy decomposition analyses. For this, supramolecular circular chains of up to 12 molecules were built with the aim of checking the capability of diazine molecules to detect SO2/SO3 compounds within the atmosphere. Trends in the interaction energies with the increasing number of molecules are mainly determined by the Pauli steric repulsion involved in these σ-hole/π-hole interactions. But more importantly, despite the assumed electrostatic nature of the involved interactions, the covalent component also plays a determinant role in its strength in the involved chalcogen bonds. Noticeably, π-hole interactions are supported by the charge transfer from diazines to SO2/SO3 molecules. Interaction energies in these supramolecular complexes are not only determined by the S···N bond lengths but attractive electrostatic and orbital interactions also determine the trends. These results should allow us to establish the fundamental characteristics of chalcogen bonding based on its strength and nature, which is of relevance for the capture of sulfur oxides.

Ultra-stable Pickering liquid crystal-in-water emulsions decorated with thermoresponsive soft microgels and their response to aqueous analytes

This work presents an extensive investigation of the Pickering stabilization of liquid crystal (LC)-in-water emulsions using soft nanometer-sized colloidal poly(N-isopropylacrylamide) (PNIPAM) microgel particles and the responsivity of the PNIPAM microgel-stabilized Pickering LC droplet-based assembly towards amphiphilic analytes. The evolution of size and stability of LC droplets with microgel concentration are found to be dependent on the emulsifier-regime. Despite microgel coating, the LC-water interface remains accessible to model analytes such as anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB). The analytes can pass through the interfacial pores and/or meshes of porous microgels to induce a bipolar-to-radial ordering transition within the droplets. The dose-response behaviour is largely influenced by the initial microgel concentration, type of analytes and interfacial layer (charge), and the number of droplets exposed to the analytes. The PNIPAM microgel-coated LC droplets notably exhibited enhanced sensitivity under conditions promoting electrostatic attractive interactions between the interfacial microgel layer and analytes. Overall, the results highlight the potential of Pickering LC-in-water emulsions for reliable and quantitative analysis of aqueous analytes, thus opening up new avenues toward the development of droplet-based optical sensors.

Amphichdiral enhancement on singlet oxygen generation and stable thallium immobilization using iron-driven copper oxide

Thallium (Tl) as a prominent priority contaminant in aquatic environment necessitates rigorous regulation. However, limited horizon devotes the impact of selective oxidation on the process of thallium purification. In this study, selective active radical of singlet oxygen (1O2) was continually generated for Tl(Ⅰ) oxidation accomplished with efficient Tl(Ⅲ) immobilization using iron-driven copper oxide (CuFe)/peroxymonosulfate (PMS). Fe-doping changed the active center of electronic structure for enhancing the catalytic and adsorptive reactivities, and installed magnetism for solid-liquid separation. Rapid reaction rate (0.253 min−1) coupled with vigorous elimination efficiency (98.32%) relied on electrostatic attraction, surface complexation, and H-bond interaction. EPR and XPS analyses demonstrated that the synergistic effects of ≡ Cu(Ⅰ)/≡Cu(Ⅱ) and ≡ Fe(Ⅲ)/≡Fe(Ⅱ) redounded to the sustained generation of 1O2 through the pathway of PMS → •O2− → 1O2, and 1O2 exploited an advantage to selectively oxidize Tl(Ⅰ) to Tl(Ⅲ). 3D isosurface cubic charts revealed that the immobilizing ability of Tl(Ⅲ) hydrate for CuFe was notably superior to that of Tl(Ⅲ) hydrate for CuO and Tl(Ⅰ) hydrate for CuO/CuFe, which further attested surface reactivity promoted stable immobilization form. This work develops the continuous generation of 1O2 and stable immobilization with the goal of efficiently cleansing Tl-containing wastewater.

Removal of PFAS by hydrotalcite: Adsorption mechanisms, effect of adsorbent aging, and thermal regeneration

Layered double hydroxides (LDH) have been shown to be effective adsorbents, but their utility for the treatment of per- and polyfluoroalkyl substances (PFAS) in water has not been fully explored. In this study, the adsorption of 9 PFAS on hydrotalcite (HT), a type of LDH, was investigated using reaction solutions with environmentally relevant PFAS concentrations. The adsorption of individual PFAS by HT depended upon a range of factors, including the temperature used to pre-treat (i.e., calcine) the HT, aging conditions, and the presence of anions in the solution. HT calcined near 400 °C most effectively adsorbed PFAS, but its ability to adsorb PFAS was sensitive to storage conditions. The adsorption of CO2 and moisture from air, which likely resulted in the re-intercalation of CO32− into the interlayer regions of HT, was observed to reduce PFAS adsorption and may explain performance loss over time. The adsorption trend among 9 PFAS and the influence on this process by Cl−, NO3−, SO42−, and CO32− indicated that adsorption occurred via a combination of ion exchange, electrostatic attraction, and hydrophobic interactions, although the relative importance of each mechanism deserves further investigation. During this study, we also demonstrated for the first time that HT can be thermally regenerated at 400 °C without affecting its ability to adsorb PFOS and PFBA. Overall, our results suggest that HT may serve as an effective alternative for PFAS treatment.

Enhancing the Catalytic Activity of Laccase@Copper-Metal-Organic Framework Nanofractal Microspheres: Synergistic Contribution of the Mass Transfer and Electron Transfer Pathway.

Metal-organic frameworks (MOFs) are limited by small pores and buried active sites, and their enzyme-like catalytic activity is still very low. Herein, laccase was employed as the organic component to construct laccase@Cu3(BTC)2 nanofractal microspheres. During the preparation process, laccase adsorbed Cu2+ by electrostatic attractive interaction, then combined with Cu2+ by coordination interaction, and finally induced the in situ growth of H3BTC2 in multiple directions by electrostatic repulsion. Interestingly, electrostatic repulsion was tuned efficiently by adjusting the Cu2+ concentration to obtain laccase@Cu3(BTC)2 nanofractal microspheres (nanosheet microspheres, nanorod microspheres, and nanoneedle microspheres). Laccase@Cu3(BTC)2 nanorod microspheres exhibited the highest catalytic efficiency, which was 14-fold higher than that of smooth microspheres. The mechanism of the improvement of catalytic activity in the degradation of BPA was proposed for the first time. The enhanced catalytic activity depended on the adsorption effect of the nanorod framework and dual cycle synergistic catalysis of Cu+/Cu2+ active sites, which accelerated substrate diffusion and electron transfer. The catalytic mechanism of enzyme@MOF nanofractal microspheres not only deepens our understanding of enzyme and MOF synergistic catalysis but also provides new insights into the design of catalysts.

Exploring the Interfacial Hydrogen Transfer between Pt and the Siliceous Framework and Its Promotional Effect on the Isotope Catalytic Exchange.

Interfacial hydrogen transfer between metal particles and catalyst supports is a ubiquitous phenomenon in heterogeneous catalysis, and this occurrence on reducible supports has been established, yet controversies remain about how hydrogen transfer can take place on nonreducible supports, such as silica. Herein, highly dispersed Pt clusters supported on a series of porous silica materials with zeolitic or/and amorphous frameworks were prepared to interrogate the nature of hydrogen transfer and its promotional effect on H2-HDO isotope catalytic exchange. The formation of zeolitic frameworks upon these porous silica supports by hydrothermal crystallization greatly promotes the interfacial hydrogen bidirectional migration between metal clusters and supports. Benefiting from this transfer effect, the isotope exchange rate is enhanced by 10 times compared to that on the amorphous counterpart (e.g., Pt/SBA-15). In situ spectroscopic and theoretical studies suggest that the defective silanols formed within the zeolite framework serve as the reactive sites to bind HDO or H2O by hydrogen bonds. Under the electrostatic attraction interaction, the D of hydrogen-bonded HDO scrambles to the Pt site and the dissociated H on Pt simultaneously spills back to the electronegative oxygen atom of adsorbed water to attain H-D isotope exchange with an energy barrier of 0.43 eV. The reverse spillover D on Pt combines with the other H on Pt to form HD in the effluent. We anticipate that these findings are able to improve our understanding of hydrogen transfer between metal and silica supports and favor the catalyst design for the hydrogen-involving reaction.

Preparation of biomass carbon dots/carboxymethyl cellulose-based fluorescent hydrogel: Combines selective detection and visual adsorption for Copper(II)

Abstract In this study, we used nitrogen-doped carbon dots (NCDs), which were synthesized via the hydrothermal method of corn-stover biomass as raw material and polyethyleneimine (PEI) as the nitrogen source, introduced them into the carboxymethyl cellulose-based hydrogel to prepare an environmentally friendly fluorescent cellulose-based hydrogel (NCDs/CMC-PAM). NCDs/CMC-PAM was also used for simultaneous fluorescence monitoring and removal of Cu (II) in aqueous solution. The chemical and physical structures, adsorption behaviors and fluorescent properties of NCDs/CMC-PAM were investigated. The results showed that NCDs/CMC-PAM exhibited a well-linear response range of fluorescence response for Cu (II) (0∼100 μM, detection limit of 3.42 μM). NCDs/CMC-PAM showed maximum adsorption capacities of 237.71 mg/g for Cu (II), the adsorption process followed the Langmuir isotherm model and pseudo-second-order kinetic model, which is an exothermic spontaneous reaction with an increase in entropy. It can still maintain 79.03% of the original adsorption capacity after six cycles (pH=6). The adsorption mechanisms of NCDs/CMC-PAM for Cu (II) are intraparticle diffusion, electrostatic attraction, ion exchange, and ligand interaction. Hence, the present study provides a new green way to synthesize an adsorbent that can be applied for the adsorption and detection of heavy metal ions.

Influence of biochar on the removal of Microcystin-LR and Saxitoxin from aqueous solutions

The present study assessed the effective use of biochar for the adsorption of two potent HAB toxins namely, Microcystin-LR (MCLR) and Saxitoxin (STX) through a combination of dosage, kinetic, equilibrium, initial pH, and competitive adsorption experiments. The adsorption results suggest that biochar has excellent capabilities for removing MCLR and STX, with STX reporting higher adsorption capacities (622.53–3507.46 µg/g). STX removal required a minimal dosage of 0.02 g/L, while MCLR removal needed 0.4 g/L for > 90%. Similarly, a shorter contact time was required for STX removal compared to MCLR for > 90% of toxin removed from water. Initial pH study revealed that for MCLR acidic conditions favored higher uptake while STX favored basic conditions. Kinetic studies revealed that the Elovich model to be most suitable for both toxins, while STX also showed suitable fittings for Pseudo-First Order and Pseudo-Second Order in individual toxin systems. Similarly, for the Elovich model the most suited kinetic model for both toxins in presence of each other. Isotherm studies confirmed the Langmuir–Freundlich model as the best fit for both toxins. These results suggest adsorption mechanisms including pore filling, hydrogen bonding, π–π interactions, hydrophobic interactions, electrostatic attraction, and dispersive interactions.

Synthesis of weak cation exchange/C18 bifunctional magnetic polymers for pretreatment and determination of glufosinate and its two metabolites in plasma samples

This study focuses on the purification and detection of glufosinate (GLUF) and its metabolites N-acetyl GLUF and MPP in plasma samples. A Dikma Polyamino HILIC column was used for the effective retention and separation of GLUF and its metabolites, and the innovative addition of a low concentration of ammonium fluoride solution to the mobile phase effectively improved the detection sensitivity of the target analytes. Monodisperse core-shell weak cation exchange (WCX)/C18 bifunctional magnetic polymer composites (Fe3O4@WCX/C18) were prepared in a controllable manner, and their morphology and composition were fully characterized. The Fe3O4@WCX/C18 microspheres were used as a magnetic solid-phase extraction (MSPE) adsorbent for the sample purification and detection of GLUF and its metabolites in plasma samples combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). The purification conditions of Fe3O4@WCX/C18 microspheres for GLUF and its metabolites in spiked plasma samples were optimized to achieve the best MSPE efficiency. The purification mechanisms of the target analytes in plasma samples include electrostatic attraction and hydrophobic interactions. Furthermore, the effect of the molar ratio of the two functional monomers 4-VBA and 1-octadecene in the adsorbent was optimized and it shows that the bifunctional components WCX/C18 have a synergistic effect on the determination of GLUF and its metabolites in plasma samples. In addition, the present study compared the purification performance of the Fe3O4@WCX/C18 microsphere-based MSPE method with that of the commercial Oasis WCX SPE method, and the results showed that the Fe3O4@WCX/C18 microsphere-based MSPE method established in this work had a stronger ability to remove matrix interferences. Under optimal purification conditions, the recoveries of GLUF and its metabolites in plasma were 87.6–111 % with relative standard deviations (RSDs) ranging from 0.2 % to 4.8 %. The limits of detection (LODs, S/N≥3) and limits of quantification (LOQs, S/N≥10) were 0.10–0.18 μg/L and 0.30–0.54 μg/L, respectively. The MSPE-LC-MS/MS method developed in this study is fast, simple, accurate and sensitive and can be used to confirm GLUF intoxication based not only on the detection of the GLUF prototype but also on the detection of its two metabolites.